This disclosure relates to a method for treating a subterranean well formation to stimulate the production of hydrocarbons and, more particularly, such an apparatus and method for fracturing and squeezing the well formation.
Several techniques have evolved for treating a subterranean well formation to stimulate hydrocarbon production. For example, hydraulic fracture acidizing methods have often been used according to which a portion of a formation to be stimulated is isolated using conventional packers, or the like, and a stimulation fluid containing gels, acids, sand slurry, and the like, is pumped through the well bore into the isolated portion of the formation. The pressurized stimulation fluid pushes against the formation at a very high force to establish and extend cracks on the formation. However, the requirement for isolating the formation with packers is time consuming and considerably adds to the cost of the system.
Also, squeezing methods have been used which involve introducing stimulation fluids containing acids to carbonate type formations at a pressure that is higher than the formation pressure (but not as high as the fluid pressure in the fracturing methods), causing the fluid to infiltrate the pores in the formation and react with the formation to enlarge the pores. However, this is a relatively slow process and produces relatively small openings in the formation. Also, since these stimulation fluids are usually very reactive, especially at elevated temperatures, the fluid is often prematurely spent close to the wellbore in the formation. Thus, no extended reach is achieved and the fluidentry point is often greatly enlarged. As a result, it is impossible to form multiple, relatively long, and effective acid fingering throughout the wellbore face, especially in low-permeability reservoirs that require deep penetration.
Chemical reactivity of the acid can be reduced using many ways, and one of them is the use of foams. Since foams are also good leak off prevention material, they help in creating large fractures. Conventionally, foaming equipment is provided on the ground surface that creates a foam, which is then pumped downhole. Foams, however, have much larger friction coefficients and reduced hydrostatic effects, both of which severely increase the required pressures to treat the well.
Therefore, what is needed is a stimulation treatment that combines most or all features of the above types according to which the need for isolation packers is eliminated, the foam generation is performed in-situ downhole, the depth of penetration improved, and the reaction of the fracturing acid with the formation is controlled so that premature reaction of the acid with the formation is prevented.
According to an embodiment of the present invention, the techniques of acid fracturing and squeezing are combined to produce an improved stimulation of the formation. To this end, a stimulation fluid is discharged through a workstring and into a formation at a relatively high impact pressure and velocity without the need for isolation packers to fracture the formation.